I will try to post a picture tomorrow. They are pretty straight forward though. I have done a little digging through my references and believe I made an error. At one time the bores were stamped with several different designations for bore sizes based on standard plugs. For 12 gauge the went from 13/1 for .712 to (I believe) 12/? for .740. It was not uncommon to see barrels of different sizes. At later dates the actual bore size of each barrel is shown to 3 digits and the 12 in diamond with a C was used to show the chamber was to standard dimensions. I'm not sure of the date of this running change, but I suspect it had been a continuing problem as to reproof. When the multiple plugs were used, the tightest plug that would pass was marked as the bore size, but it was not an exact fit necessarily. The proof law required it to be reproved if it was enlarged over .010", but the initial marking was not exact. The more modern versions of the proof law changed to what is on this gun; 12 and C in a diamond for chamber, BNP under crown for nitro proof, three digit bore size stamp, 1-1/8 lead charge, 3 tons/square inch, 2-1/2" chamber length and a crossed swords date code with ZB for 1974 and a 2to designate the inspector.
I started at the point of thinking it was a 1915 to 1920 gun and in the era of multiple plugs. It turns out what is there is exactly correct for an original proof from 1974 with no added work. I am going to measure the bores and wall thicknesses tomorrow to be safe. At the worst I suspect the barrels may be polished but the measurements will tell.
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